1. Field of the Invention
The present invention relates to photoresist compositions and more particularly, it relates to photoresist compositions which have excellent coating uniformity and stain inhibitory properties after coating so that they can be easily applied to real industrial fields and which can improve working environments due to the reduction of amounts to be consumed, the decrease of time to be required for manufacture, etc. when manufactured on a large scale.
2. Description of Related Art
In order to form fine circuit patterns such as liquid crystal display device circuits or semiconductor integrated circuits, insulated membranes or conductive metal membranes formed on substrates are coated with photoresist compositions, and then the coated photoresist compositions are exposed to light in the presence of a mask having a prescribed configuration and then developed to form a pattern of a desired configuration. Thereafter, the metal membranes or insulated membranes are etched using the photoresist membranes on which the patterns are formed, as a mask and then, the remaining photoresist membranes are eliminated to form fine circuits on the substrates.
In general, spin coating or slit coating methods are employed for the above-mentioned coating. These coating methods have merits in that they enable the formation of uniform photoresist membranes. The coating uniformity is a scale to show how uniform the thickness of coated photoresists is on entire substrates, and the higher the coating uniformity is, the more easily safe properties can be secured in subsequent processes. Consequently, large quantities of solvents were consumed to form uniform, stain-free photoresist membranes.
Generally, the photoresist compositions comprise polymeric resins, photosensitive compounds and solvents, and numerous attempts have been made to improve the coating uniformity, photographic speed, development contrast, and human safety.
In particular, U.S. Pat. No. 3,666,473 discloses the use of mixtures of two phenolformaldehyde novolak resins and typical photosensitive compounds, U.S. Pat. No. 4,115,128 discloses addition of organic acid cyclic anhydrides to phenolic resins and naphtoquinone diazide photoresists to increase photographic speed, and U.S. Pat. No. 4,550,069 discloses use of novolak resins and o-quinone diazide photosensitive compounds, and propylene glycol alkyl ether acetate as a solvent to increase coating uniformity and photographic speed and to improve human safety.
Further, various solvents have been developed in spin coating methods for the improvement of the properties of photoresist compositions for liquid crystal display devices and working stability and for example, they include ethyleneglycol monoethyletheracetate, propyleneglycol monoethyletheracetate, ethyllactate, and so on. However, ethyleneglycol monoethyletheracetate was known to have serious side effects against human safety, propyleneglycol monoethyletheracetate has inferiority due to pin marks after baking process in jumbo substrates such as TFT-LCD and also has lowered flatness when used as a sole solvent, and in case of the use of ethyllactate, adhesion of the compositions to substrates is poor and it is difficult to obtain uniform coating.
In case of slit coating methods, since there is no centrifugal force as in spin coating methods, solvents with excellent flatness are required for uniform coating properties.
Therefore, there are still demands on photoresist compositions suitable for each individual industrial field without sacrificing any one of the preferred properties of photoresist compositions such as coating uniformity, coating stain properties, photographic speed, rate of residual membranes, development contrast, resolution, solubility of polymeric resins, adhesion to substrates and circuit line width uniformity.